Capacitive touch surface need to be free from contamination to work properly. Capacitive touch sensing in certain environments, however, exposes the touch surface to liquids or other materials that contaminate the surface and have a negative effect on the sensing characteristics. Hence, there is a need for capacitive touch sensing that is not influenced by contamination of the touch surface, in particular water on the touch surface.
Existing solutions for water resistance in capacitive sensing use mutual capacitance only and cause a negative shift on the signal when water is introduced to the system, and a positive shift when a finger is introduced. When water is removed from the system, a false trigger can occur if removing the negative shift causes too large of a positive shift.
Other solutions to this problem use a software pattern-matching algorithm to detect the difference in behavior between water and a finger. This leads to large overhead and the possibility that not all patterns of behavior have been considered.